The influence of liquid environments on the mechanical characteristics of surface failure in naturally-occurring fluorapatite single crystals (FAP) and dental ceramics (DC) under sliding will be investigated. It is postulated that the surface failure of these materials is influenced by the mutual interactions of mobile charge carriers and dislocations within the near-surface lattice. It is further postulated that the distribution of these mobile charge carriers will be governed in part by an adsorption phenomenon, the electrical double layer (EDL), resulting from the presence of the liquid. Adsorption-induced changes have been proposed as a mechanism for mechanical behavior in crystalline ceramics and glass. In the present study, the EDL between FAP and DC and various liquids will be studied using an electroosmotic pressure technic. Specifically, the zeta- potential, which quantitatively describes the diffuse mobile layer portion of the EDL, will be measured. The magnitude and sign of the zeta-potential of various environments will then be evaluated in a factorial design with replications as to their influence on the surface failure of FAP and DC under single-pass sliding in these environments. The wear apparatus will consist of a surface grinder, loading jug, tangential force transducer, sapphire hemispherical slider, and sample holder. Three dependent variables (track width, tangential force, and failure classification) will be evaluated with the aid of analysis of variance and multiple comparisons. The proposed study should contribute to a better understanding of the wear behavior of enamel, by characterizing the wear behavior of a simplified system that may serve as a model for human enamel.